Typically, a folding closure has one section which unfolds from one side of an opening to closure the opening or two sections which unfolds from opposite sides of the opening. The free end of each section has a locking post that locks the section in the unfolded, closed position. One manner of locking the post in the closed position is to provide a lock bolt slidable in the bottom of the post for movement out of the post to enter a hole in the floor. Usually a second lock rod is also provided in the top of the post for movement out from the post into a hole in the top of the opening.
The closure sections are suspended by trolleys from an overhead rail in the opening and have a small clearance from the floor when moved between open and closed positions. The lock bolts usually extend a predetermined length from the end of the locking post when in the locked position. The extended length is normally sufficient to insert the rod deep enough into the hole in the floor that it cannot be removed by lifting the post.
When installing the closure, it is often found that the floor and/or the top of the opening are not level. For example, the area where the locking post is located when the closure section is open may be lower than the surrounding floor. The difference may result in the lock bolt not extending sufficiently into the opening to securely lock the section.
To overcome the problem of uneven floors, it has been known to thread the lock bolt in a lock bolt unit in the bottom of the post and use an adjustment nut to change the distance the rod extends out of the end of the post. The nut is fixed in position but can be rotated in either direction to raise or lower the bolt. Thus the distance the lock bolt extends from the end of the post can be adjusted. An example of such an adjustment arrangement is shown in U.S. Pat. No. 4,944,169, issued to Robert Labelle. However, it can be difficult to rotate the adjustment nut to adjust the distance the bolt extends out of the end of the post because of space limitations. In accordance with the present invention, a lock bolt unit is provided, the length of which can be adjusted without having to adjust the lock bolt. The present invention further provides guide means for the lock bolt unit making it easier to install and to operate.